{
    let a = 1
    console.log(a)
}
// console.log(a) //访问不到

var b = 3
let c = 4;
c = 5;
console.log(b, c) //输出3 5
console.log(window.b, window.c) //输出3 undefined

var b = 4;
console.log(b)

// let c = 5;
// console.log(c) //let声明过的变量不能重复定义 Identifier 'c' has already been declared

// let有的特性const都有,const定义的是常亮不能被修改

// const a = 2;
// const b;
// b=3 //不被允许